1. Field of the Invention
This invention relates to non-skid surface compositions applied to the surface of a material. More particularly, this invention is directed to silica containing non-skid surface compositions applied to paper products such as paperboard and most particularly prepared from reprocessed or recycled paper.
2. Description of the Prior Art
Recycled paper has traditionally been manufactured on slow cylinder machines forming the paper at a speed of 100 to 250 feet/minute. Formerly, the products resulting from such processes were used largely as speciality items, such as shirt backs, cartons, folders, etc. As the trend of recycling has increased, recycled paper in small percentages has started to appear in linerboard used in container manufacturing. Recently, the development of high speed cylinder machines such as the Escher-Wysch German machine, as well as innovations permitting the use of shorter recycled fibers on conventional high speed Fourdrinier machines, has allowed recycled fiber to command an increasing share of linerboard production. Today, there are many mills which are capable of manufacturing paper products containing between 60% and 100% recycled fiber and some which employ as little as approximately 10% recycled fiber. The use of such a large percentage of recycled fiber in the finished paper has led to increasing problems in the handling of the paper, both in the mill and at converters, because of its increased slipperiness. This loss in the coefficient of friction is due to the shorter fibers which result from the additional processing required by recycling as compared to virgin paper fibers, as well as from contaminants introduced with the used paper. These contaminants include dirt, wax, cold and hot melt adhesives, water proofing, and other special coatings, etc. Various paper fiber processing techniques have been employed to remove some of these contaminants prior to paper formation but have had only marginal success in removing the wax-like contaminants which cause the paper to become slippery. Thus, the combination of shorter recycled fibers and wax-like contaminants have had a detrimental effect on the finished linerboard coefficient of friction, or slip-angle, as it is commonly measured by the TAPPI method. For instance, virgin linerboard will generally have TAPPI-method slip-angles of between 20.degree. and 25.degree.. Typical linerboard made with a modicum of recycled fiber will have slip-angles of from 15.degree. to 20.degree., and some boards having a high percentage of recycled fibers, and their concomitant contaminants, can have slip-angles of between 10.degree. and 15.degree.. Slip-angles of less than 20.degree. are the cause of several paper handling problems. First, in the paper mill itself it may be difficult to rewind the sheet as it would tend to "wander" along the reel. Additionally, when clamp trucks attempt to lift finished rolls of paper for shipping, the center of the reel may telescope out. In a paperboard plant, such as one which produces corrugated board or forms containers from such materials, additional problems arise since it is difficult to keep the corrugator running in-line as the board tends to "wander". Frequently, the finished boxes are so slippery that they cannot be moved around the plant or to a customer without difficulty.
Traditionally, this problem has been solved by applying a dispersion of a colloidal silica non-skid agent by any one of a number of application methods. In lower speed machines, a water box application has been successfully used. In high speed machines, the colloidal silica has been applied as a surface coating by the "size" press in the paper mill. More commonly, however, a series of low pressure sprays apply the material to the sheet as it is being wound on its final reel. While these methods have enjoyed some success, the increased cost of materials and processing have diminished the financial savings anticipated as a result of using recycled paper.